So-called straddle connectors are used for connection by a surface mount technology (SMT) method to the edges of circuit boards having on both surfaces electrical traces. Such straddle connectors have two rows of electrical contacts, and an edge of the circuit board having electrical traces formed on both surfaces is inserted between the contact sections of the straddle connector. The contacts are connected to corresponding electrical traces using soldering practices known in the art.
An example of a conventional straddle connector 100 is shown in FIG. 5, which has a number of electrical contacts 102 arranged in two rows in an insulating housing 101. Under normal conditions, contact sections 103 of the contacts 102 are inclined toward each other due to their resilience so that the distance between the soldering sections 104 of the sections 103 is less than the thickness of the circuit board 110 together with the conductive pads 111, 112 and solder coatings 113, 114 attached to them. After straddle connector 100 is placed over the edge of the circuit board 110, contact sections 103 are soldered to corresponding conductive pads 111, 112 using an infra red beam or other method of heating.
The conventional straddle connector 100 shown in FIG. 5 suffers from a disadvantage that when it is mounted on the circuit board 110, contact sections 103 can scrape solder coatings 113, 114 off conductive pads 111, 112. This problem originates from the fact that the distance between the soldering sections 104 of contact sections 103 is smaller than the thickness of the circuit board 110. It is obvious that if the distance between the soldering sections 104 is larger than the thickness of the board, it will be impossible to solder them to conductive pads 111, 112 via solder coatings 113, 114 even when they are heated. If the solder coatings 113, 114 are scraped off, appropriate soldering of the soldering sections 104 to the conductive pads 111, 112 cannot be achieved. Therefore, the reliability of the soldered connections is substantially compromised.
A number of efforts and attempts were made to improve reliability of the SMT methods. One of such methods is described in Japanese Patent Publication No. 1991-257776. According to this publication, in order to achieve a complete connection of the contacts of a connector having one row of SMT contacts, the contacts, or leads, at the time of connection of the connector to a circuit board, are deflected or shifted away from the conductive pads and after alignment are pressed against them. For this purpose, in one specific embodiment, lugs are provided in the opening of the connector for the insertion of the circuit board into the connector, and the circuit board has depressions whose locations correspond to the lugs. If the SMT contacts are arranged in two rows, the front ends of the contact are deflected outwardly to make the gap between them wider than the thickness of the circuit board using the lugs and depressions.
Another conventional method is described in Japanese Utility Model Publication No. 1992-78787. In the connector described therein, solder tails of the contacts arranged in two rows are arranged in one row. The connector is mounted to the edge of a circuit board in a pivoted manner. Therefore, the contacts do not exert pressure on the solder coatings on the conductive pads of the circuit board until it is completely mounted, thus avoiding scraping off the solder coatings.
However, the straddle connectors described above still have some disadvantages. For example, in the first design, it is difficult to deflect all soldering sections of the contacts uniformly if the connectors have many contacts, thus making it difficult or impossible to attain reliable connection of all contacts. The straddle connector of the second design has a disadvantage in that it is not suitable for high-density-mounting applications by SMT methods to circuit boards with electrical traces on both surfaces.